1. Field of the Invention
The present invention relates to a power supply for the development of a regulated DC output and more particularly to a device that has very small losses and thus high operating efficiency. This highly efficient regulation is maintained over wide load variation and is capable of being shorted without damage or the excessive loss of energy.
2. Brief Description of Prior Art
The use of switching regulators for the conversion and regulation of direct current in power supply applications is become more and more universal. The primary advantage of these devices is that by switching at high speeds, regulation may be accomplished with small light weight components. This is accomplished at a considerably higher efficiency than is normally experienced with the series pass regulator where an element is inserted between the source of DC energy and the load impedence of the element is automatically adjusted to supply the appropriate output current and voltage. Such a series regulation method requires that substantial energy be dissipated in the series regulator. In the switching regulator, the switching device is either all the way on or all the way off. Thus its losses are limited to the switching losses and the on state forward voltage drop losses.
Switching losses are dependent upon the amount of current flowing through the switching element at the time it is turned off or on, as well as the amount of time it takes to do so and how often it is done. Thus it may be said the loss is directly proportional to the current at switching time and frequency. These losses are normally still substantially less than that of the series pass element. Even with the improved efficiencies, it is considered a good design if only 20% of the energy is lost in the regulating circuits. Many commercially available units lose as much as 30% of the input power in the process of transforming the power while regulating. Switching losses develop too much heat in the switching element and subject it to damage when the voltage across it and the current through it exceed a particular point at the same time. In order to increase reliability by removing the heat from the switching device, a snubbing network consisting of a resistor and a capacitor, and often a diode bypassing the resistor, is connected across the switching element to absorb the switching energy at the time the element turns off. The snubber does not do anything to increase the efficiency of the circuit it merely removes the loss from the switching device and improves its reliability. In fact, the efficiency is actually reduced by the snubber since the value of the capacitor must be selected for the worst case of operation. A 20 to 30% heat loss also normally requires that the power supply be made larger to incorporate a heat sink or radiating device. Larger power handling supplies may require air or water cooled heat sinks for the switching element snubbing network resistor.